On 2007-04-29 13:35:37 +0100, (Andrew
Gabriel) said:

In article ,
Andy Hall writes:
However, in the winter, the mains water is at 5 - 8 degrees. Shower
water temperature is 40 degrees. Combis are rated in terms of flow
rate for a 35 degree temperature rise. Therefore, the flow rate at
the shower will be that of the combi.

A 30kW combi will manage about 12 litres/min under these circumstances.
A worthwhile shower is at 15lpm and above, so a 38kW combi is really
needed to achieve that.

This puzzles me. I had a 30kW non-thermostatic multipoint.
It was too powerful for a shower. Turning the flow rate up
to get the water cool enough not to be painful resulted in
rather painful high pressure jets, and water squirting out
past all the O-ring seals. (It's been replaced by one with
some thermostatic control since then, which is also 30kW
and works brilliantly.)

Yebbut.....

If the water is at 5 degrees this can be true.

At 5 degrees, it's limited to the physics.

Of course it does depend on the shower head. One can get a shower
head with needle jets that will scarify the skin at 10lpm. Not
comfortable though.